An electromagnet, which is characterized by having a two-piece yoke to which a nonmagnetic substance is stuck fast and held, and forming a pair of magnetic poles, has been proposed (see, e.g., Patent Document 1). The electromagnet is designed to separate a coil portion from harmful surroundings, and also work as an electromagnetic by dividing the yoke into two portions with the nonmagnetic substance that is stuck fast and held.
A magnetic core, which forms a magnetic circuit in part of a magnetic path, has been proposed (see, e.g., Patent Document 2). The magnetic core consists of magnetic composite material portions and a high magnetic flux density material portion. The magnetic composite material portions are formed of magnetic composite materials that are placed on both end sides of the magnetic circuit. The high magnetic flux density material portion is formed of a high magnetic flux density material having a higher magnetic flux density and a lower specific resistance than those of the magnetic composite material portions. The high magnetic flux density material portion is tightly sandwiched between the magnetic composite material portions in the direction of the magnetic path of the magnetic circuit.
A plunger, which includes a coil bobbin, a coil, and a yoke, and in which a resin is poured between the yoke and the coil bobbin applied with the coil, has been proposed (see, e.g., Patent Document 3). The plunger is formed as follows: The diameter W2 of a second flange is set smaller than the diameter W1 of a first flange (W1>W2). The second flange is disposed on an open end side of the yoke, and the coil is wound between the first and second flanges in a tapered shape.
An electromagnetic device having high gain and high phase frequency characteristic that is used for an actuator such as a magnetic bearing device has been proposed (see, e.g., Patent Document 4). The electromagnetic device is provided with a stainless steel that surrounds the magnetic yoke supporting a target object by magnetic attraction without touching it.    Patent Document 1: Unexamined Japanese Patent Publication No. Hei 4-208504 (see FIG. 1)    Patent Document 2: Unexamined Japanese Patent Publication No. 2005-150308 (see FIG. 1)    Patent Document 3: Unexamined Japanese Patent Publication No. Hei 6-295817 (see FIG. 1)    Patent Document 4: Unexamined Japanese Patent Publication No. Hei 5421228 (see FIG. 1)